The invention relates to chain saws and more particularly to clutches for chain saws.
It is common practice to drive the saw chain of a chain saw by an engine through a centrifugal clutch which operates in response to rotation above a predetermined speed to drivingly connect a chain drive sprocket to the engine. Such clutches are often arranged to permit some slippage in the event the saw chain becomes squeezed in the kerf or otherwise is restrained from movement. This restraining force on the chain frequently can be greater than the force transmitted from the engine to the chain and can result in damage to the chain, the engine or intervening components. Such forces develop so rapidly that conventional centrifugal clutches often cannot react or disengage rapidly enough to avoid damage to the chain saw.
Representative examples of prior chain saw centrifugal clutch constructions are disclosed in the following U.S. Pat. Nos.:
Kiekhaefer: 2,675,835 issued Apr. 20, 1954 PA0 Irgens: 3,144,890 issued Aug. 18, 1964 PA0 Deelman: 3,339,596 issued Sept. 5, 1967 PA0 Linkfield: 3,519,037 issued July 7, 1970 PA0 Mattsson: 3,664,390 issued May 23, 1972 PA0 Densow: 3,818,533 issued Mar. 14, 1974 PA0 Arff: 3,849,884 issued Nov. 26, 1974. PA0 Connell: 2,728,252 issued Dec. 27, 1955 PA0 Amtsberg: 2,881,888 issued Apr. 14, 1959 PA0 Lill: 3,035,675 issued May 22, 1962 PA0 Paterson et al: 3,435,931 issued Apr. 1, 1969.
Attention is also directed to the following U.S. Pat. Nos.: